Feeding device working in stepwise manner



g- 1966 a. E. FOGELFQTRGM ETAL 3,253,573

FEEDING DEVICE WORKING IN STEPWISE MANNER Filed April 13, 1964 3Sheets-Sheet 1 g- 1966 c5. E. FOGELSTR5M ETAL 3,253,573

FEEDING DEVICE WORKING IN STEPWISE MANNER Filed April 15, 1964 5Sheets-Sheet 2 INVENTOR Qsn E, Faun 5mm BY 5%? -eck 60mm Q42 2 424 Am:uEY

g-' 1966 G. E. FOGELSTROM ETAL. 3,263,573

FEEDING DEVICE WORKING IN STEPWISE MANNER Filed April 15, 1964 3Sheets-Sheet 5 3 MW ff MmJ T c n AC V W; 3 E mm 4 as 6 0 United StatesPatent 3,263,573 FEEDING DEVICE WORKING EN STEPWHSE MANNER Giista E.Fogelstriim and Osten Erilr Carlsson, Naclra, Sweden, assignors to AtlasCopco Airtieholag, Nacka, Sweden, a corporation of Sweden Filed Apr. 13,1964, Ser. No. 358,996 Claims priority, application Sweden, Apr. 16,1963, 4,113/63 10 Claims. '(Cl. 91-217) This invention relates tofeeding devices for rock drills and more particularly to feeding devicesof the type working in stepwise manner by the aid of a reciprocatingmotor and a number of stepping or locking members thereon providinguni-directional locking action against the feed bar or shell on whichthe rock drill is movable, such locking action being reversible by meansof reversing elements associated with the locking members.

In feeding devices of this type the reversing elements hitherto havebeen operable independently of each other and have been shifted whollymanually, which has demanded the operator to be present at the forwardend of the feed bar each time when it comes to the point of returningthe feeding device to the starting position. This renders simultaneoushandling of multiple drills diflicult and it is an important object ofthe invention to make possible automated return or rearward feed of thefeeding device. Another object of the invention is to provide a certaindependency in operation between the reversing elements in that shiftingof one of the reversing elements from forward to rearward feed bringsabout shifting of the other reversing element to the rearward feedposi-.

tion, whereas shifting of the other reversing element from forward torearward feed position will still be independent of the first mentionedreversing element, leaving the latter in the forward feed position. Astill further object of the invention is to provide a simple andeffective reversing mechanism for the locking members whereby the members for purposes of making automated shifting more easy can be shiftedby a relatively small angular movement of the reversing elements.

'The foregoing and further objects and advantages of the presentinvention will become apparent hereinafter as this description proceeds,reference being made to the accompanying drawings in which an embodimentof the invention is illustrated by way of example and by which theinvention is not to be considered limited as it may be carried out inmany dilferent ways within the scope of the claims. In the drawings FIG.1 is a top view of a feed bar and a rock drill provided with the feedingdevice according to the invention, FIG. 2 is a side view of thearrangement in FIG. 1. FIG. 3 shows the feeding device in FIG. 2 in aforward position on the feed bar and shifted for return. FIG. 4 showsthe feeding device in FIG. 2 in starting position on the feed bar. FIG.5 shows on a larger scale a longitudinal sectional view through thefeeding device with the cylinder and piston means in extended position.FIG. 6 shows the feeding device in FIG. 5 in contracted position. FIG. 7is a top view of the feeding device in FIG. 5. FIG. 8 is a fragmentaryside View of the rear locking member in FIG. 5. FIG. 9 shows a sectionon the line 9-9 in FIG. 5. FIG. 10 shows the locking member in FIG. 8after it has received an opposite inclination by the reversing element.FIG. 11, finally, shows the locking member in FIG. 9 with the reversingelement in a second position of adjustment.

In the figures the feeding device is generally designated by the numeral2a and consists of a cylinder 21 in which a slidable piston 22 istightly guided. The cylinder 21 carries a front cover 23 and a rearcover 24 which to- Patented August 2, 1966 ice gether with a back piece26 are connected to the cylinder 21 by means of through tensioning bolts25. A piston rod 27 is connected to the piston 22. and projects to therear through a guide sleeve 28 in the back piece 26. A sealing ring 29in the back piece tightens against the piston rod 27.

A tubular distributing slide 34 is slidably guided in suitable bores inthe rear cover 24 and piece 26 between the end positions depicted inFIGS. 5 and 6. The distributing slide 30 surrounds the piston rod 27with a considerable clearance and is provided with an inner flange 31. Aring 32 aflixed to the piston rod 27 adjacent the piston 22 engages theflange 31 just prior to the piston 22 reaching the end position depictedin FIG. 5, at which instant the distributing slide 30 is shifted to theposition shown in FIG. 5. Furthermore the piston rod 27 has a shoulder.33 which in its turn engages the inner flange 31 just prior to thepiston 22 reaching the end position depicted in FIG. 6, at which instantthe dis tributing slide 34} is shifted to the position shown in FIG. 6.

Pressure fluid is supplied via a conduit 35 to a nipple 36 on theunderside of the rear cover 24 and is conducted from the nipple througha bore 37 to the outer surface of the distributing slide 30. In theposition shown in FIG. 5 pressure fluid then passes the through holes 39and acts thanks to the clearance between the distributing slide 3t} andthe piston rod 27 under full pressure on the rear face of the piston 22,at which instant the piston rod is moved into the: cylinder 21 and thefeeding device 20 is contracted. Pressure fluid disposed in front of thepiston 22 is expelled through a pas sage 4S and a wide peripheral groove40 in the distributing slide to an outlet 38. After shifting of thedistributing valve 3% as shown in FIG. 6, pressure fluid is conductedfrom the bore 37 via the Wide groove 40 to the passage 48 leading to thefront face of the piston 22. The piston rod 27 is then moved outwardlyfrom the cylinder 21 and the feeding device 2a is extended thereby.Simultaneously herewith the chamber behind the piston 22 is emptiedthrough the interior of the distributing slide 34B and the outlet 33which has been opened by the rear edge, of the distributing slide 3d. Aslong as pressure fluid is supplied to the conduit 35 and the bore 37,the feeding device 20 evidently will perform extensions and contractionsfollowing in automatic succession one upon the other, since shifting ofthe distributing slide 30 will take place by means of the ring 32 andthe shoulder 33 each time the piston 22 reaches proximity of therespective end positions.

A rod 41 disposed coaxially with respect to the piston rod 27 projectsfrom the front cover 23 in forward direction. A boss 42 is carried byeach of the rods 27 and 41, which bosses carry through parallel axles43. About each axle 43 there is pivotally affixed a locking member orplate 44. The two locking plates 44 support themselves against a feedbar 45 for a rock drill and form locking members displaceable along thefeed bar. These locking plates are provided for carrying the feedingdevice 20 and have a unidirectional reversible locking action, to bedescribed hereinafter, in the longitudinal direction of the bar. Thefeed bar 45 has two coplanar parallel guide flanges 46 and each lockingplate is provided with slots 47 turned in opposite directions, intowhich slots the flanges 46 project. The width of the slots 47 is chosensomewhat greater than the thickness of the flanges 46, by reason ofwhich the locking plate can tilt between two outer positions, shown inFIG. 8 and FIG. 10, respectively, which-are inclined in oppositedirections with respect to the feed bar. In these outer positions theslots 47 evidently will clamp the flanges 46 providing a frictionalengagement between the locking plate 44- and the flanges 46 if theinclination of the locking plate is increased by force actuation on theaxle 43 in one axial direction of the feed bar. If on the other hand theaxle will be actuated by a force tending to decrease the inclination ofthe locking plate, the locking plate 44 will be able to slide freelyalong the flanges 46. In the outer position shown in FIG. 8 a forceactuation on the axle 43 to the right evidently will lock the lockingplate 44 to the feed bar 45, which is indicated by dot and dash lines,whereas a force actuation to the left will cause the locking plate 44 toslide freely to the left. Thus one receives a uni-directional lockingaction to the right and free movability of the locking plate to theleft. In the outer position depicted in FIG. one receives in analogyherewith uni-directional locking action and free movability in oppositedirections.

A pair of reversing elements are arranged for positioning the lockingplates 44 to the alternative outer positions. Each of the reversingelements consists of a housing 50 turnably arranged at one side of therespective locking plates 44 on the piston rod 27 and the rod 41,respectively. The housing 50 is turnable between two positions ofadjustment defined by a transverse pin 52, which projects radially fromthe respective rods 41 and 27 and by coaction with a groove 53 in thehousing 50 limits the turning motion of the latter. A pair ofdiametrically opposed elastic biasing or spring means directed axiallytowards the appurtenant locking plate 44 and consisting of springpressed plungers 54, 55 are provided in the housing 50. The plungers 54,55 are biased by compression springs 56 axially in outward directionfrom the housing 50 engaging the locking plate 44 at the upper as wellas at the lower side of the axle 43. A shoulder 57 on each plunger 54,55 restricts the axial projection thereof by engaging the inner wall ofthe housing 50. In order that the diametrically opposed plungers 54, 55shall be able to move the locking plate 44 into inclined outer position,either of the plungers must be thrown out of operation. This isaccomplished by two dimples 58, 59 disposed at an angular distance fromone another somewhat smaller than 180 degrees, which dimples areprovided on the side of the locking plate 44 facing the plungers. Thedimples 58, 59 are disposed in such manner than the plunger 55 of thereversing element 50 falls into the dimple 59 in the forward feedposition of the reversing element 50 shown in FIG. 9. This throws theplunger 55 out of operation while the opposed plunger 54 continues topush against the upper part of the locking plate 44 thereby moving theplate into the inclined position for forward feed shown in FIG. 8. Whenthe reversing element is turned to its rearward feed position shown inFIG. 11, the plunger 55 leaves the dimple 59 and pushes the lower partof the locking plate 44 while the opposed plunger 54 falls into theupper dimple 58 and is thrown out of operation thereby. The inclinationof the locking plate 44 will then be according to FIG. 10.

The reversing elements 50 are provided with operating handles 60projecting in lateral direction. Chamfered portions 61 are provided atone side of each of the dimples 58, 59 for making the passage of therespective plungers 54, 55 to and from the dimples more easy. As soon asthe plunger 54 with its spring 56 under certain compression duringshifting from forward to rearward feed reaches the chamfered portion 61of the dimple 58, the spring force acting on the plunger 54 thereforewill assist in turning the reversing elements 50 the remaining angle totheir fully shifted position, which final turning is performed undercompression of the spring acting on the other plunger 55. Thanks to thecloseness of the empty dimple to the adjacent active plunger the fullturning angle during shifting will be small. The two reversing elements50 on the respective rods 51 and 27 are mounted with the plungers turnedaway from each other. Since the handles 60 as well as the locking plates44 in the two positions of adjustment preferably should be parallel theplungers on the reversing element which is sitting on the rod 41 aremounted upside down with respect to the reversing element 50 and itsplungers on the piston rod 27. For making possible exchangeabilitybetween the locking plates 44 and correct cooperation with therespective reversing elements, the locking plates 44 are provided withopposed slots 47 in paired symmetrical disposition as depicted in FIGS.9 and 11.

To one of the handles 60, for example to the forward handle, there isaflixed a coupling rod 62 which extends to and under the other handle60. When the forward handle is swung upwards the coupling rod 62simultaneously therewith will move the rear handle to the other positionof adjustment upwards whereby both reversing elements 50 are moved fromforward to rearward feed position.

On the flanges 46 in front of the feeding device 20 there is slidablyguided a slide 65. On a transverse pivot 67 carried by an upstandingbracket 66 on the slide 65 there is in conventional manner affixed adrill 68 carrying a drill steel 69. A conventional drill steel guide 70may be provided forwardly on the feed bar 45 for guiding the drill steel69.

To the rear end of the slide 65 is fixed an upstanding plate 71, FIGS. 5and 7, having a central hole 72 therethrough. The rod 41 of the feedingdevice 20 projects into the hole 72 and at opposite sides of the plate71 there are arranged annular rubber buffers 73 around the rod 41.Thrust plates 74, which are axially afiixed to the rod 41, are arrangedoutside the rubber buffers 73 alternately pushing each against one ofthem when the feeding device moves in forward or rearward directionalong the feed bar 45. The hole 72 surrounds the rod 41 with aconsiderable clearance, due to which fact the feeding device 20 will besupported substantially solely by the two locking plates 44.

From a suitable pressure source, not shown, pressure fluid is suppliedvia a conduit 78 to a two way valve 79 fixed to the rear end of the feedbar 45. In the open position of the valve 79 shown in FIG. 2, a pressurefluid is conducted to a hose 80 and thence to the open main valve 81 ofthe rock drill 68, the main valve being indicated diagrammatically onlyin the figures. Pressure fluid from the main valve drives the hammermotor (not shown) of the rock drill. Via a passage 82 a portion of thepressure fluid is branched to passages passing through the transversepivot 67 and thence onto the bracket 66 and the conduit 35, whereby thefeeding device receives pressure fluid and starts operation.

At a suitable location on the forward end of the feed bar 45 there isaffixed a cam plate 83 which by means of a bolt 84 can be fixed in aselective position to holes 85 on the feed bar 45. The cam 83 isarranged to cooperate with the coupling rod 62 or the forward handle 60on the feeding device 20.

In the position shown in FIG. 2 the feeding device 20 thus receivespressure fluid and its piston 22 is brought into reciprocation while thehammer motor of the rock drill 68 is operating. With the reversingelements 50 and the locking plates 44 in the position shown in FIG. 2and FIGS. 59, the successive extensions and contractions of the feedingdevice 20 will produce a successive stepwise displacement of the feedingdevice 20 in forward direction along the feed bar 45. The rear thrustplate 74 of the feeding device 20 transmits the feeding force, which isdefined by the pressure in the cylinder 21 in front of the piston 22, tothe plate 71 of the slide 65 via the rear rubber buffer 73. The pressurein front of the piston 22 displaces the cylinder 21 and the rod 41 inforward direction while the forward locking plate 44 slides along theflanges 45. As soon as the drill 69 has penetrated into the rock adistance corresponding to a full throw of the piston, the distributingslide 30, FIG. 5 will be shifted, whereby the piston 22, the piston rod27 and the rear locking plate rapidly will be brought forward to theposition shown in FIG. 6. During such movement the forward locking plate44 forms a support for the feeding force by locking against the feed bar45. As the drilling work progresses the rock drill 68 is thus fed inforward direction. When the desired drilling depth has been reached thefeeding device 20 will approach the cam plate 83, which will turn theforward handle 60 from the forward feed position corresponding to FIG. 9to the rearward feed position corresponding to FIG. 11. Simultaneouslyherewith the coupling rod 62 will turn the rear handle 60 to the sameposition of adjustment, whereby the inclination of both locking plates44 is shifted in the manner hereinbefore described. Such shifting willbe performed easily thanks to the small turning angle necessary forshifting and to the assistance provided by the springs 56 of theplungers 54. In the new position of the reversing elements 50 andlocking plates 44 shown in FIGS. 3, 4 10 and 11, the successiveextensions and contractions of the feeding device will produce astepwise return of the feeding device back to the starting position onthe feed bar 45 under the action of a pulling force on the slide 65defined by the pressure behind the piston 22. Return is finished in FIG.4 and at this instant the coupling rod 62 encounters the valve 79 andmoves it to cut-off position. The pressure fluid supply to the drill 68as well as to the feeding device 20 is interrupted hereby and operationof these parts ceases.

When a new working cycle is to be started, the operator depresses therear handle 60, FIG. 4, whereby the coupling rod 6-2 and the forwardhandle 60 simultaneously are pushed down to a position corresponding toforward feed. The locking plates 44 will now again take up theinclination shown in FIG. 2. Simultaneously herewith the two-way valvecan be opened without hindrance, FIG. 2, which alternatively may beperformed manulally or by spring action, at which instant the newworking cycle is started.

What we claim is:

1. A feeding device for rock drills comprising an elongated feed bar forslidably supporting a rock drill therealong, a pair of locking membersmovably mounted on said feed bar, adjustable means on said lockingmembers providing in a first position of adjustment uni-directionallocking against said feed bar to allow forward and to prevent rearwardmovement of said members along said feed bar and in a second position ofadjustment unidirectional locking against said feed bar to allowrearward and to prevent forward movement of said members, a pressurefluid operated extensible and contractable feed motor connected to saiddrill and movable therewith, said motor including cooperating cylinderand piston elements coupled one to each of said locking mem bers formoving said members and thereby said rock drill step by step along saidfee-d bar by successive extensions and contractions of said motor in thedirection defined by the position of adjustment of said adjustablemeans, means for automatically controlling the delivery of pressurefluid to said motor for continuously extending and contracting saidcylinder and piston elements, first and second reversing elementsmovably mounted on said motor each adjacent one of said locking membersfor movement between a forward and a rearward feed position and havingmeans thereon for moving said adjustable means from their first to theirsecond position of adjustment as a result of said reversing elementsbeing moved from said forward to said rearward feed position, said firstreversing element being journalled for movement from said forward tosaid rearward feed position independently of said second reversingelement for purposes of rendering said feed motor inactive by causingopposite locking action of said members, and coupling means connected tosaid second reversing element and engageable with said first reversingelement for moving the latter from said forward to said rearward feedposition in unison with said second reversing element.

2. A feeding device according to claim 1 in which there are provided cammeans on said feed bar cooperating with said reversing elements and saidcoupling means for mechanically shifting said reversing elements inunison from said forward to said rearward feed position upon saidfeeding device having moved a predetermined feed length, and means foradjusting the longitudinal position of said cam means on said feed bar.

3. A feeding device according to claim 2 in which a pressure fluidsupply line is connected to said drill and there is provided a cut offvalve in said line rearwardly on said feed bar actuatable to cut off thefluid supply to said rock drill, and an abutment on said feed motorcooperating with said out off valve for causing actuation thereof uponsaid feeding device having moved back said feed length.

4. A feeding device according to claim 1 in which each locking memberconsists of a locking plate pivotally mounted about an axle disposed onsaid feed motor transversely with respect to said feed bar, said lockingplate being pivotable about said axle between two outer positionsinclined in opposite directions with respect to said feed bar, clampingsurfaces on each locking plate frictionally cooperating with said feedbar in said outer positions thereby to provide said uni-directionallocking in forward and rearward direction, respectively, a pair ofbiasing means on each said reversing element disposed adjacent eachlocking plate at opposite sides of said axle and pushing against saidlocking plate for pivoting it about said axle, and means for throwingrespectively one or the other of said opposite biasing means out ofoperation for providing forward or rearward feed, respectively,depending on the feed position of said reversing elements.

5. A feeding device according to claim 4 in which there are providedangularly spaced dimples on said locking plates at opposite sides ofsaid axle for alternately receiving said biasing means, wherebyrespectively one or the other of said biasing means is thrown out ofoperation.

6. A feeding device according to claim 1 in which said reversingelements are journalled for turning movement about an axis disposedlongitudinally of said feed bar, an operating handle on each reversingelement, and a longitudinal coupling rod connected to one of saidhandles and engageable with said other handle for shifting said handlesand thereby said reversing elements in unison from said forward to saidrearward feed position.

7. A feeding device for rock drills comprising an elongated feed bar forslidably sup-porting a rock drill therealong, a pair of locking membersmovably mounted on said feed bar and supporting themselves thereon,adjustable means on said locking members providing in a first positionof adjustment uni-directional locking against said feed bar to allowforward and to prevent rearward movement of said members along said feedbar and in a second position of adjustment unidirectional lockingagainst said feed bar to allow rearward and to prevent forward movementof said members, a pressure fluid operated extensible and contractablefeed motor disposed longitudinally of said feed bar, said motorincluding cooperating cylinder and piston elements coupled one to eachof said locking members for being carried thereby on said feed bar andfor moving said members step by step along said feed bar by successiveextensions and contractions of said motor in the direction defined bythe position of adjustment of said locking members, means forautomatically controlling the delivery of pressure fluid to said motorfor continuously extending and contracting said cylinder and pistonelements, a connection between said feed motor and said rock drill fortransmitting the step by step movement of said feed motor to said rockdrill, said connection having means providing relative movabilitybetween said drill and said feed motor transversely to the longitudinaldirection of said feed bar to permit said feed motor to rest solely onsaid locking members, first and second reversing elements movablymounted on said motor each adjacent one of said locking members formovement between a forward and a rearward feed position and having meansthereon for moving said adjustable means from their first to theirsecond position of adjustment as a result of said reversing elementsbeing moved from said forward to said rearward feed position, and meansfor synchronizing the movement of said reversing elements from saidforward to said rearward feed position.

8. A feeding device according to claim '7 in which there are providedcam means on said feed bar cooperating with said reversing elements andsaid synchronizing means for mechanically shifting said reversingelements in unison from said forward to said rearward feed position uponsaid feeding device having moved a predetermined feed length, and meansfor adjusting the longitudinal position of said cam means on said feedbar.

9. A mechanism movable by fluid power step by step in either directionalong an elongated support comprising a pair of locking members movablymounted on said support and supporting themselves thereon, adjustablemeans on said lock-ing members providing in a first position ofadjustment uni-directional locking against said support to allow forwardand to prevent rearward movement of said members along said support andin a second position of adjustment uni-directional locking against saidsupport to allow rearward and to prevent forward movement of saidmembers, a pressure fluid operated extensible and contractable motordisposed longitudinally of said support and carried solely by saidlocking members thereon, said motor including cooperating cylinder andpiston elements coupled one to each of said locking members at theopposite ends of said motor for being carried by said members on saidsupport and for moving said members step by step along said support bysuccessive extensions and contractions of said motor in the directiondefined by the position of adjustment of said adjustable means, meansfor automatically controlling the delivery of pressure fluid to saidmotor for continuously extending and contracting said cylinder andpiston elements, first and second reversing elements movably mounted onsaid motor each adjacent one of said locking members for movementbetween a forward and a rearward position and having means thereon formoving said adjustable means from their first to their second positionof adjustment as a result of said reversing elements being moved fromsaid forward to said rearward position, and means for synchronizing themovement of said elements from said forward to said rearward feedposition.

10. A mechanism according to claim 9 in which each locking memberconsists of a locking plate pivotally mounted about a horizontal axledisposed on said motor transversely with respect to the longitudinaldirection of said support, said locking plate being pivotable about saidaxle between two outer positions inclined in opposite directions withrespect to said support, clamping surfaces on each locking platefrictionally cooperating with said feed bar in said outer positionsthereby to provide said uni-directional locking in forward and rearwarddirection, respectively, a pair of biasing means on each said reversingelement disposed adjacent each locking plate at opposite sides of saidaxle and pushing against said locking plate for pivoting it about saidaxle, and means for throwing respectively one or the other of saidopposite biasing means out of opera-tion for providing forward orrearward movement of said motor, respectively, depending on the positionof said reversing elements.

References Cited by the Examiner UNITED STATES PATENTS 1,297,925 3/1919Stage 92-15 1,740,683 12/1929 Gartin 9215 1,909,179 5/1933 Huffman 921613,160,074 12/1964 Leander et al. 91-217 SAMUEL LEVINE, Primary Examiner.

P. E. MASLOUSKY, Assistant Examiner.

1. A FEEDING DEVICE FOR ROCK DRILLS COMPRISING AN ELONGGATED FEED BARFOR SLIDABLY SUPPORTING A ROCK DRILL THEREALONG, A PAIR OF LOCKINGMEMBERS MOVABLY MOUNTED ON SAID FEED BAR, ADJUSTABLE MEANS ON SAIDLOCKING MEMBERS PROVIDING IN A FIRST POSITION OF ADJUSTMENTUNI-DIRECTIONAL LOCKING AGAINST SAID FEED BAR TO ALLOW FORWARD AND TOPREVENT REARWARD MOVEMENT OF SAID MEMBERS ALONG SAID FEED BAR AND IN ASECOND POSITION OF ADJUSTMENT UNIDIRECTIONAL LOCKING AGAINST SAID FEEDBAR TO ALLOW REARWARD AND TO PREVENT FORWARD MOVEMENT OF SAID MEMBERS, APRESSURE FLUID OPERATED EXTENSIBLE AND CONTACTABLE FEED MOTOR CONNECTEDTO SAID DRILL AND MOVABLE THEREWITH, SAID MOTOR INCLUDING COOPERATINGCYLINDER AND PISTON ELEMENTS COUPLED ONE TO EACH OF SAID LOCKING MEMBERSFOR MOVING SAID MEMBERS AND THEREBY SAID ROCK DRILL STEP BY STEP ALONGSAID FEED BAR BY SUCCESSIVE EXTENSIONS AND CONTACTIONS OF SAID MOTOR INTHE DIRECTION DEFINED BY THE POSITION OF ADJUSTMENT OF SAID ADJUSTABLEMEANS, MEANS FOR AUTOMATICALLY CONTROLLING THE DELIVERY OF PRESSUREFLUID TO SAID MOTOR FOR CONTINUOUSLY EXTENDING AND CONTRACTING SAIDCYLINDER AND PISTON ELEMENTS, FIRST AND SECOND REVERSING ELEMENTSMOVABLY MOUNTED ON SAID MOTOR EACH ADJACENT ONE OF SAID LOCKING MEMBERSFOR MOVEMENT BETWEEN A FORWARD AND A REARWARD FEED POSITION AND HAVINGMEANS THEREON FOR MOVING SAID ADJUSTABLE MEANS FROM THEIR FIRST TO THEIRSECOND POSITION OF ADJUSTMENT AS A RESULT OF SAID REVERSING ELEMENTSBEING MOVED FROM SAID FORWARD TO SAID REARWARD FEED POSITION, SAID FIRSTREVERSING ELEMENT BEING JOURNALLED FOR MOVEMENT FROM SAID FORWARD TOSAID REARWARD FEED POSITION INDEPENDENTLY OF SAID SECOND REVERSINGELEMENT FOR PURPOSES OF RENDERING SAID FEED MOTOR INACTIVE BY CAUSINGOPPOSITE LOCKING ACTION OF SAID MEMBERS, AND COUPLING MEANS CONNECTED TOSAID SECOND REVERSING ELEMENT AND ENGAGEABLE WITH SAID FIRST REVERSINGELEMENT FOR MOVING THE LATTER FROM SAID FORWARD TO SAID REARWARD FEEDPOSITION IN UNISON WITH SAID SECOND REVERSING ELEMENT.